SPIKE SYNCHRONIZATION AND RATE MODULATION DIFFERENTIALLY INVOLVED IN MOTOR CORTICAL FUNCTION

It is now commonly accepted that planning and execution of movements a re based on distributed processing by neuronal populations in motor co rtical areas. It is less clear, though, how these populations organize dynamically to cope with the momentary computational demands. Simulta neously recorded activities of neurons in the primary motor cortex of monkeys during performance of a delayed-pointing task exhibited contex t-dependent, rapid changes in the patterns of coincident action potent ials. Accurate spike synchronization occurred in relation tcr external events (stimuli, movements) and was commonly accompanied by discharge rate modulations but without precise time locking of the spikes to th ese external events. Spike synchronization also occurred in relation t o purely internal events (stimulus expectancy), where firing rate modu lations were distinctly absent. These findings indicate ?hat internall y generated synchronization of individual spike discharges may subserv e the cortical organization of cognitive motor processes.